Java ProcessBuilder: Resultant Process Hangs

user_313141 0
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I've been trying to use Java's ProcessBuilder to launch an application in Linux that should run "long-term". The way this program runs is to launch a command (in this case, I am launching a media playback application), allow it to run, and check to ensure that it hasn't crashed. For instance, check to see if the PID is still active, and then relaunch the process, if it has died.

The problem I'm getting right now is that the PID remains alive in the system, but the GUI for the application hangs. I tried shifting the ProcessBuilder(cmd).start() into a separate thread, but that doesn't seem to be solving anything, as I hoped it would have.

Basically the result is that, to the user, the program APPEARS to have crashed, but killing the Java process that drives the ProcessBuilder.start() Process actually allows the created Process to resume its normal behavior. This means that something in the Java application is interfering with the spawned Process, but I have absolutely no idea what, at this point. (Hence why I tried separating it into another thread, which didn't seem to resolve anything)

If anyone has any input/thoughts, please let me know, as I can't for the life of me think of how to solve this problem.

Edit: I have no concern over the I/O stream created from the Process, and have thus taken no steps to deal with that--could this cause a hang in the Process itself?

processbuilder crash multithreading linux java
10 Answers

Another solution is to start the process with Redirect.PIPE and close the InputStream like this:

ProcessBuilder builder = new ProcessBuilder(cmd);
builder.redirectOutput(Redirect.PIPE);
builder.redirectErrorStream(true); // redirect the SysErr to SysOut
Process proc = builder.start();
proc.getInputStream().close(); // this will close the pipe and the output will "flow"
proc.waitFor(); //wait

I tested this in Windows and Linux, and works!

user_14704360

I believe the problem is the buffering pipe from Linux itself.

Try to use stdbuf with your executable

new ProcessBuilder().command("/usr/bin/stdbuf","-o0","*executable*","*arguments*");**

The -o0 says not to buffer the output. The same goes to -i0 and -e0 if you want to unbuffer the input and error pipe.

user_63645960

you need to read the output before waiting to finish the cycle. You will not be notified If the output doesn't fill the buffer. If it does, it will wait until you read the output.

Suppose you have some errors or responses regarding your command which you are not reading. This would cause the application to stop and waitFor to wait forever. A simple way around is to re-direct the errors to the regular output.

I was spent 2 days on this issue.

public static void exeCuteCommand(String command) {
    try {
        boolean isWindows = System.getProperty("os.name").toLowerCase().startsWith("windows");
        ProcessBuilder builder = new ProcessBuilder();
        if (isWindows) {
            builder.command("cmd.exe", "/c", command);
        } else {
            builder.command("sh", "-c", command);
        }
        Process process = builder.start();
        BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream()));
        String line;
        while ((line = reader.readLine()) != null)
            System.out.println("Cmd Response: " + line);
        process.waitFor();
    } catch (IOException e) {
        e.printStackTrace();
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}
user_45840310
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